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Biochemistry Exam #2 > HMP Shunt/Fructose & Galactose Metabolism > Flashcards

HMP Shunt/Fructose & Galactose Metabolism Flashcards

1
Q

What is the starting substrate > product of the Oxidative branch? What is the rate limiting enzyme, and what does it convert?

A

Glucose 6P > Ribose 5P

G6PD converts Glucose 6P > 6P Gluconolactone

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2
Q

What is the starting substrate > product of the Forward Non-oxidative branch? What is the enzyme used, and what does it convert?

A

Ribose 5P > Fructose 6P + Glyceraldehyde 3P

Transketolase converts Xylulose 5P > Fructose 6P + Glyceraldehyde 3P

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3
Q

What is the purpose of the Forward Non-oxidative branch?

A

Convert Ribose 5P to glycolytic intermediates (Fructose 6P and Glyceraldehyde 3P) when the body’s Ribose 5P needs are low - these glycolytic intermediates are eventually oxidized

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4
Q

What is the starting substrate > product of the Reverse Non-oxidative branch? What is the enzyme used, and what does it convert?

A

Fructose 6P + Glyceraldehyde 3P > Ribose 5P

Transketolase converts Fructose 6P + Glyceraldehyde 3P > Xylulose 5P

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5
Q

What is the purpose of the Reverse Non-oxidative branch?

A

Produce Ribose 5P when the body’s needs are high, without having to produce NADPH too (body’s needs for NADPH are low)

  • Note: if the body needs both Ribose 5P and NADPH, it will use the Oxidative branch
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6
Q

What is the coenzyme utilized by Transketolase? What is Transketolase influenced by?

A

TPP

Influenced by substrate availability (no regulation)

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7
Q

What accumulates in the cytosol during the fed state and what does it lead to an accumulation of upstream? Why is this?

A

Citrate(cyto) accumulates - Citrate is an inhibitor of PFK-1 so this causes an accumulation of G6P (upstream of the PFK-1 step)

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8
Q

Where is accumulated G6P sent to and what does it help to produce?

A

G6P is shunted to the HMP Shunt where it produces NADPH via the Oxidative branch

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9
Q

What four processes require NADPH as an energy source?

A
  • FA Synthesis
  • Cholesterol Synthesis
  • Steroid Synthesis
  • Glutathione Reduction
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10
Q

In tissues with mitochondria, what source(s) is NADPH derived from? What about in tissues without mitochondria?

A

With mitochondria: Malic Enzyme and HMP Shunt

Without mitochondria: HMP Shunt only

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11
Q

What are the tissues without mitochondria?

A
  • RBCs
  • Cornea
  • Lens
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12
Q

How does NADPH provide electrons for the reduction of hydrogen peroxide?

A

2 GSH (reduced) provide electrons to H2O2 to create two H2O > NADPH then provides electrons to convert GSSG (oxidized) back to GSH

G6PD uses NADP+ when it converts Glucose 6P to 6P Gluconolactone, which converts NADP+ back to NADPH

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13
Q

What are three major dietary sources of fructose?

A
  • Disaccharide sucrose
  • Free fructose in fruits, veggies, honey
  • High fructose corn syrup
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14
Q

Is the entry of fructose into cells insulin-dependent?

A

NO, fructose metabolism is NOT insulin-dependent

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15
Q

What are the two steps in fructose metabolism? What are the enzymes used in each step?

A
  1. Fructose > Fructose 1P via Fructokinase

2. Fructose 1P > DHAP + Glyceraldehyde via Aldose B

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16
Q

What are DHAP and Glyceraldehyde converted into and what processes is this product used in?

A

DHAP + Glyceraldehyde > Glyceraldehyde 3P

Glyceraldehyde 3P is used in glycolysis and lipogenesis

17
Q

Is the rate of fructose metabolism faster or slower than glucose metabolism and why?

A

Fructose metabolism is more rapid because it bypasses PFK-1, the rate-limiting step in glycolysis

18
Q

How does high dietary fructose affect TAG synthesis?

A

High dietary fructose leads to high TAG synthesis via lipogenesis

19
Q

What is the first step in galactose metabolism? What is the enzyme used in this step?

A
  1. Galactose > Galactose 1P via Galactokinase
20
Q

What is the second step in galactose metabolism? What is the enzyme used in this step?

A
  1. Galactose 1P + UDP Glucose > UDP Galactose + Glucose 1P via Galactose 1P Uridyltransferase
21
Q

What may UDP Galactose be converted to (third step of galactose metabolism) before it can proceed with metabolism? What is the enzyme used in this step?

A

UDP Galactose > UDP Glucose via UDP-Hexose 4-Epimerase

22
Q

What is the fate of UDP Glucose produced in the third step of galactose metabolism?

A

UDP Glucose can…

  • Participate in intermediary metabolism
  • Convert another Galactose 1P into UDP galactose (second step)
23
Q

What is the alternative fate of UDP Galactose produced from the second step of galactose metabolism?

A

UDP Galactose can be used to synthesize lactose, glycoproteins, glycolipids, and glycosaminoglycans

24
Q

When galactose levels are continuously high due to galactose metabolism disorders, what enzyme converts galactose to an alcohol? What is the name of the this alcohol produced?

A

Galactose > Galactitol via Aldose Reductase

Biochemistry Exam #2 (5 decks)

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